1. Field of the Invention
This invention relates to the recovery of nitramines from aluminized energetic materials. This invention is particularly useful for recovering nitramines from aluminized energetic materials such as solid propellants, explosives, and pyrotechnics.
2. State of the Art
Energetic materials have found widespread use, perhaps no more extensively than in military applications, where energetic materials are used to make composite propellants for ballistic missiles and explosive compositions for munitions and ordnances. An example of a propellant commonly found in rocket motors and missiles is Class 1.1 solid propellants. Like most other energetic materials used in military applications, Class 1.1 solid propellants are formed from a composition comprising a combination of one or more of the following: polymeric binders, plasticizers, ballistic additives, chemical stabilizers, curing agents and catalysts, metal powders, and inorganic and/or organic oxidizers.
Demilitarization in the United States and abroad has created a need for an economical, reliable, non-hazardous, and environmentally friendly method for disposing of the stockpile of surplus tactical missiles and explosives existing worldwide. Additionally, a growing number of larger rocket motors, such as intercontinental ballistic missiles (ICBMs), are being and will have to be demilitarized due to international treaties, such as the START treaties. The disposal of such energetic materials is the subject of various publications and U.S. patents, including U.S. Pat. No. 4,231,822 to Roth and U.S. Pat. No. 4,661,179 to Hunter et al. However, these U.S. patents focus on disposing of explosive materials by “desensitizing” or “destroying” the materials.
The degradation of energetic materials into an unusable state is not the most economical alternative of disposal, since many energetic materials are both expensive and reusable. For example, one class of organic oxidizer that has found wide acceptance in the rocket propulsion, explosive, and pyrotechnic arts comprises nitramines. Common nitramines include, for example, cyclotetramethylenetetranitramine (also known as HMX and 1,3,5,7-tetranitro-1,3,5,7-tetraaza-cyclooctane), cyclotrimethylenetrinitramine (also known as RDX and 1,3,5-trinitro-1,3,5-triaza-cyclohexane), TEX (4,10-dinitro-2,6,8,12-tetraoxa-4,10-diazatetracyclo-[5.5.0.05,903,11]-dodecane), HNIW (also known as CL-20) (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo[5.5.0.05,903,11]-dodecane), and combinations thereof. Nitramines are commonly among the most expensive and highly energetic ingredients of conventional energetic compositions. Further, nitramines are sometimes present in energetic compositions in relatively high concentrations, such as on the order of up to about 50% by weight of solid rocket motor propellants and up to about 98% by weight of explosives. These factors make the successful and efficient recovery of nitramines in high yields for subsequent re-use highly desirable.
A method for the extraction and recovery of nitramine oxidizers from solid propellants is disclosed in U.S. Pat. No. 5,284,995 to Melvin, which discloses the use of a liquid ammonia extraction agent for extracting the nitramines HMX and RDX from rocket motor solid propellants. The use of liquid ammonia in nitramine recovery techniques introduces several complexities and expenses, especially in a closed system, including high capital expenditures required as outlay to obtain equipment capable of operating at the high-pressures (5 to 40 Kpsi) at which liquid ammonia is handled. The presence of liquid ammonia also creates other problems, such as worker safety issues, since contact between the ammonia and human skin can cause severe chemical burns to the handler. Additionally, liquid ammonia is combustible, and presents a severe inhalation hazard if not handled correctly. Another disadvantage of the U.S. Pat. No. 5,284,995 process is that subjecting energetic materials, such as Class 1.1 propellants containing nitramine oxidizers, to the pressurized environments described in the '995 patent increases the risk of accidental detonation, as well as the accompanying catastrophic consequences that an accidental detonation or explosion often has on human life and property. Yet another disadvantage of the process of U.S. Pat. No. 5,284,995 is that nitramines are dissolved in liquid ammonia, requiring recrystallization of the nitramines. However, the recrystallized nitramines have different particle sizes than the nitramine particles found in the propellant. Also, if recrystallization is not performed under the right conditions, the polymorph of the nitramine changes during recrystallization.
Another method for recovering ingredients from a pyrotechnic material is disclosed in U.S. Pat. No. 4,098,627 to Tompa et al., in which the pyrotechnic containing a cured polymeric binder is decomposed under mild conditions. The method involves heating the pyrotechnic material to a temperature of from about 50° C. to about 160° C. in a liquid medium comprising an active hydrogen-containing compound capable of cleaving the chemical bonds contained in the polymer. Representative liquid media include mineral acids such as hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid and perchloric acid, as well as primary amines, secondary amines, ammonia, and water. The process is expedited by modifying the liquid medium via the addition of an organic solvent. Organic solvents reportedly suitable in the process are toluene, xylene, dioxane, and tetrahydrofuran. The organic solvent functions either to swell the organic polymeric binder present in the pyrotechnic material or to dissolve filler material present in the pyrotechnic material. The decomposition technique is carried out at 80° to 120° C. In practice, however, these organic solvents raise a host of ecological and safety concerns, including flammability, VOC emissions, environmentally sound and cost-effective waste disposal, and handling expenses. Additionally, U.S. Pat. No. 4,389,265 to Tompa et al. reports that the use of mineral acids and water in the manner prescribed by the '627 patent produces low yields of about 36%. Indeed, example 5 of the '627 patent reports that under the basic conditions of its process RDX may be destroyed.
Two additional approaches for reclaiming nitramines from propellants having polymeric binders are disclosed in U.S. Pat. No. 4,389,265 to Tompa et al. The first approach utilizes a solution of 2-aminoethanol in a mixture of an aromatic solvent and an alcohol to dissolve the propellant binder. The 2-aminoethanol breaks down or dissolves the polymeric binder. Examples of aromatic solvents suitable for the first approach include benzene, toluene, xylene, ethylbenzene, and diethylbenzene. Examples of alcohols suitable for the first approach include ethanol, 1-propanol, 2-propanol, and mixtures thereof. The second approach is performed with a solution of a mineral acid other than nitric acid, an organic solvent, and water. For the second approach, examples of suitable mineral acids are hydrochloric, sulfuric and phosphoric acid; examples of organic solvents are acetone, methylethylketone, tetrahydrofuran, and mixtures thereof. The mineral acid and organic solvent combine to break down or dissolve the polymeric binder. After dissolution of the pyrotechnic binder is completed in the 2-aminoethanol or the mineral acid process, the nitramine and metals, if present, are removed by filtration and the nitramine is extracted in acetone. Although relatively high yields are reported in U.S. Pat. No. 4,389,265, the presence of aromatic and organic solvents raise ecological and safety concerns over such issues as flammability, volatile emissions, and waste disposal. Also, the nitramine is recovered with aluminum fuel particulates. Consequently, separation of the aluminum requires dissolving, filtering, and recrystallizing of the nitramine. As mentioned above, recrystallization can cause the polymorph and size of the nitramine particles to change.
U.S. Pat. No. 6,063,960 discloses the recovery of nitroamines and reformulation of by-products. The '960 patent generally focuses on non-aluminized propellants, with the exception of its mention of VTG-5A and WAY, both of which are aluminized propellants. According to the '960 patent, the propellants are treated with 60-70% nitric acid in a preferred ratio of nitric acid solution to feed of 1.0:1.0 l/kg. This feed ratio calculates to a weight ratio of less than 1.5:1. Although these conditions are adequate to recover nitramines from non-aluminized propellants containing conventional binders, in the case of an aluminized propellant a substantial proportion of aluminum would not be dissolved under these conditions. Accordingly, in the event that an aluminized propellant were treated by the '960 process, separation of the aluminum would require additional steps of dissolving, filtering, and recrystallizing of the nitramine.
Thus, it would be a significant improvement in the art to develop a method in which nitramines are recovered from aluminized energetic materials without recrystallizing the nitramines and in which there is no need for the use of either liquid ammonia under increased pressure or hazardous organic solvents that are volatile and/or flammable.